Pandaria will not feel like a real continent if the questing funnels you in a stifling linear progression the entire way.

Vanilla quests were unpredictable and the world felt immense and full of opportunity, but things were actually not coherent enough, and Blizz realized players needed a little more guidance. They achieved this and the questing design was pretty much perfect with TBC; Outland questing was sort of streamlined so that you could progress in an intuitive way, BUT there were still plenty of little quests tucked all over Outland, and it felt like a real world. This was probably the best balance for zone questing in WoW's lifespan.

Wrath was almost as good, with the welcome revelation of phasing technology, but the questing began to be a little more on-rails and a little less random and exciting. Still, Northrend was such a richly constructed place that it felt like a real place throughout.

Questing and immersion in general have taken a big step backwards in Cataclysm. The questing over-used phasing consistently IMHO, but the extreme linearity is the worst: Every zone is a thrill exactly once, the first time you do it. (And in the case of the Harrison Jones half of Uldum, it's not even much fun the first time.) Repeating the process on one or more characters reveals the weakness in the strictly linear questing, and going back to Cata zones after your first or second run-through of them can be a soul-crushing proposition.*(Here I am mainly referring to the 80-85 zones. In general I love what I've seen of the revamped zones so far, although here and there they may be too restrictive.)

I want stumbling around Pandaria to feel more like the epic experience of exploring Outland back in the day, rather than have the questing hold my hand and bring me from points A to B to C all the way through to Z.

I am kind of pessimistic about this because it seems like Blizzard will want to take the easy way out on this. But shaking up the ultra-linear questing from 85-90, adding alternate paths and giving players the option to NOT do certain quests they don't want to do, would go a long way toward bringing back some of what made WoW so much fun in the past, something we know Blizzard wants to do.

The advantages tend to flow from the effort to build epic stories for players to be a part of. When you put the player into a linear questline, you can more easily incorporate dramatic elements like foreshadowing, plot twists, and a satisfying climax that you know the player is going to be there for.

The disadvantages have been well-covered: If you're isolated into a personal story too much, you lose the sense of being in an open world that is filled with alternative potential adventures. It's more difficult to hop around and partake of the glories of several different zones at the same time, and harder to join up with friends whenever you like. Group quests become less-desirable.

As Dave Kosak and others have said before, we think we may have gone a bit too linear with Cataclysm. That informs one of our big philosophies for Mists of Pandaria: Give players more flexibility to play how they want to. We think that the solution may be to have linear story arcs, but have more of them in each zone, rather than making the whole zone one big story with a beginning, middle, and end. In addition to multiple linear quest lines, there will be smaller (and in some cases, one-off) quest hubs, and some of those hubs may be well off the beaten path.

To make that work, we've got to tweak the orientation of quest achievements. Rather than "vacuum up every single quest in the zone", we're aiming for achievements that reward completing the main story arcs. All in all, players should feel less like their time spent playing in a zone is exactly the same as every other player.